1. Technical Field
The invention relates generally to a motion transmission assembly. Particularly, the invention relates to a motion transmission assembly of the type wherein motion is transmitted along a curved path by a flexible motion transmitting core element movably supported by a flexible conduit. Specifically, the invention relates to rotary actuated motion transmission assemblies which transfer motion along a cable which circuitously extends between a control knob, and an apparatus to be controlled, specifically, a bulkhead door in a vehicle.
2. Background Information
All types of vehicles having enclosed passenger compartments, including automobiles, trucks, vans and mini-vans, continue to grow in popularity with the number of these vehicles expected to increase in the future. Vehicle manufacturers, recognizing this ever growing market, are continually striving to improve their products. These improvements include on-board computers for regulating and monitoring engine performance, improved aerodynamic design for better fuel efficiency and appearance, and computers which calculate and display by LEDs on the dashboard everything from gas mileage to the preferred trip route. Despite such advances, manufacturers have been unable to satisfactorily solve the problem of forward firewall or bulkhead doors which improperly open and close upon manual adjustment of control levers for regulating the environment in the passenger compartment. Moreover, the need has recently arisen to replace the linearly moveable control lever with a rotary style control knob which further increased the system complexity.
Most vehicles have a control module mounted on the dashboard for regulating the temperature within the passenger compartment. Other functions such as venting and defrosting of the vehicle windows are also controlled by manual adjustment of the linearly moveable module levers. The levers are connected to the bulkhead doors via cables which are movably mounted for opening and closing apertures formed in the bulkhead.
For example, in many automobiles, one of the levers of the control module is moved to the "hot" position for opening a door on the bulkhead and permitting heat to be blown into the passenger compartment during cold weather. As the lever is moved linearly from the "cold" to the "hot" position, the cable extending between the lever and door is displaced in the direction of the lever, and the door is pulled to the open position. When the lever is returned to the "cold" position the cable is displaced in the direction of the door and the door is pushed to the closed position.
Problems occur because the levers do not provide a consistent feel to the passenger as the levers are often loose through a portion of their path of travel, and are more difficult to move at other portions along the path of travel. The difference in feel is created by ever changing loads along the path of travel. These load changes are created as the weight of the bulkhead door is increasingly and decreasingly carried by the cable.
Another problem that is consistently faced by automobile manufacturers is that most of the change in air flow occurs at the beginning and the end of the door's path of travel. The door movement between these two positions or in the center of the path of travel, only minimally affect the air flow. As such, the passenger operating the control lever must operate the lever for a significant distance to affect the air flowing into the passenger compartment.
It is for these and other reasons that the vehicle manufacturers have turned away from the use of manually operated levers to actuate the doors, and are beginning to use rotary actuated knobs to transfer the motion to the bulkhead door. However, the transmission of rotary input motion, along a circuitous path to a discreet output can only occur by use of a flexible shaft, which for the variety of paths needed on the market, is too costly; or by transferring the rotary motion into linear motion.
Heretofore, the transfer has been clumsy at best as the resistance on the knob has not remained constant through the entire knob rotation. Moreover, the knobs utilized in the prior art did not always remain in the desired position. Specifically, the knobs would be heavily loaded at certain positions within the stroke, which load would cause the knob to inadvertently and undesirably rotate, such rotation would then affect movement of the bulkhead door.
Attempts to solve such problems are well known in the art and primarily have focused on the use of electric motors to turn a cable or pulley to open and close the bulkhead doors. However, such motors are much more costly than manually operated motion transmission systems and are often as much as five times more costly. Moreover, the use of motors further burdens the engine and provides more components subject to breakdown.
Therefore, a need exists for a rotary controlled motion transmission assembly which transfers rotary input motion along a linear cable which extends along a circuitous path, and which will provide for a constant resistance on a control knob through the knob's entire radius of travel. Moreover, the need exists for such a rotary assembly which input knob will remain securely positioned at any point in the knobs radius of travel, and is not overloaded in either the clockwise or counterclockwise directions. Lastly, the need exists for an assembly which can accelerate the opening of the bulkhead door in that the arc of the radius of travel where little alteration to the air flow is experienced is such that each point along the radius of travel will create the same effective change in air flow into or out of the passenger compartment.
There is no assembly for the transmission of motion of which I am aware which can be quickly and easily installed on a vehicle in an assembly production line, which controls the operation of a bulkhead door along a circuitous path while the rotatable control knob has a constant resistance thereon, and which knob will not inadvertently rotate due to overloading by the position of the bulkhead door. Moreover, there is no known assembly of which I am aware where each radial incremental turn of the control knob creates the same effective change in air flow through the entire radius of travel.